Systems are known, for example German DT-OS 20 47 586, other prior patents: U.S. Pat. No. 3, 745, 985, DT-OS No. 25 25 42 677, Ser. No. 724,976 (FF 6344) wherein the current through the primary winding of the ignition coil is interrupted if the engine has been at rest for a predetermined time interval. The current in this system is interrupted by switching an output transistor connected in series with the primary winding to the nonconductive state. In such a system, the interruption of the primary current when the engine is at rest may cause a spark to be developed which, in turn, might actually cause a small explosion which might damage the engine.